fix(task): Support for custom bower directories

Instead of duplicating the logic to find the correct bower config file and
obtain the components directory from it, this uses the config object that bower
exposes. The data no longer contains a hard-coded `components/` prefix in their
path, but instead is joined with the bower path on runtime.

/fix #16
/ref #13

@btford What do you think? Is adding `bower` as dependency worth it?